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Slits

The available slits are shown in the following table. The slit widths are given in pixels and arcsec projected on the sky. The spectral resolution is lower in a wider slit (see the grism table), even for point sources since under most atmospheric conditions the seeing wings of pointlike objects fill the wider slits. Note that for each f/6 slit width, 2 slits are available, one of which is offset from the optical axis and causes the spectrum to be shifted to shorter wavelengths on the array. Note also that the f/32 10 pixel wide slit and the f/6 2 pixel wide slit are the same slit.

Spectroscopy

Basic characteristics of T-ReCS's spectroscopy modes

T-ReCS is capable of spectroscopy with R~100 - 1000 in the 8–26 micron range as follows:

Imaging

Basic characteristics of T-ReCS's imaging mode

Taken from the current T-ReCS Intro page

Exposure times

The following five tables provide various exposure time limits. Constraints are due to a number of factors, more than one of which may need to be considered for a given NIRI configuration:

  • Minimum possible exposure time due to array electronics (Table 1)

  • Efficiency - ensuring that a much larger percentage of the time is spent exposing the array than reading it out (Table 2)

  • Time required for noise from fluctuations in the sky+telescope background to equal read noise (Table 3)

  • Maximum possible exposure time before array is saturated by background (Table 4)
  • Observation Preparation

    This section mainly describes how to prepare and check NIRI observations. Setting up observing sequences at Phase II is not intuitive until one is quite experienced (and maybe even not then). Thus, the key to successful observation preparation is starting from the NIRI OT Library.

    Guiding Options

    NIRI standalone (i.e., without AO) requires the use of a peripheral wavefront sensor for both imaging and spectroscopy. PWFS2 is preferred over PWFS1, as it can be used on fainter guide stars, can run at a higher frequency for a given guide star, works better under windy and cloudy conditions, and is smaller and thus vignettes less of the field of view.

    Spectroscopy

    Low-moderate resolution spectroscopy can be obtained either at f/6 through each of the 1-5μm windows or at f/32 (the latter usually with adaptive optics) at JHK only. A variety of slit widths are available. The properties of the slits, grisms, and blocking filters are decribed in the section. The f/6 and f/32 pixel scales in spectroscopy mode are the same as those in imaging mode.

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